yoke ball link adjustment

[Bobs]

I'm building an Intrepid gas, standard boom. I have all my linkages connected up to and including the washout assembly. With everything at exactly 90 degrees, including the elevator control bar perfectly lined up with the main shaft, I noticed that the swashplate is slightly tilted forward. My question is this: can I adjust the links on the front and back of the yoke arms to get the swashplate perfectly level? By adjusting the front link one full turn out and the back link one full turn in, the swashplate is then perfectly level. Will this cause any binding or is this in fact the way to level the swash? Thanks.

[ShawnK]

It would seem that you have some uneven length linkages somewhere. If it were my helicopter, I would take the entire head assembly off and start again at Square One.

There's a good chance that the ball links coming off your elevator control arms are not the same length. Check the length of each arm from the center of the hinge pin on the yoke to the center of the ball link. Most likely, those two numbers will be different. Adjust them so that they're equal.

Now, make your aileron links (the ones going from the bellcranks to the swashplate) exactly the same length as the elevator links. Now you know that your swash will sit square in relation to the elevator and aileron controls.

After doing that, reinstall your head assembly and take a good look at it again. Since the "porkchop" links (the one-piece plastic links going from the swashplate to the washout arms) are a fixed length, there's nothing you can do about them. But, make sure that the flybar control links (the ones going from the washout arms to the flybar control arms) are the same length, and that your flybar control arms are level.

Basically, make sure that each link on the head is the same length as it's opposing counterpart (there are two of each link on the head). If you started with straight parts, built it with equal length opposing links in all the right places, build everything "90 and square", and your Bell-Hiller mixing arms are level at zero degrees pitch, then you'll have a properly assembled head.

If everything above the swash is 90 and square, but your swash is tilted, then the problem is most likely your elevator links. But if you change those, your head won't be 90 and square anymore. You have to go back and forth for a bit to get all this stuff worked out, but that's just the joy of owning a helicopter. :mrgreen:

[Malorie]

Just adjust the linkages at the elevator servo to compensate.

The slight off condition is more than likely due to the broached hole either in the elevator arm or the elevator yoke is very slightly off from 90 degrees.

You don't want to adjust it out at either the swashplate linkages or the links between the elevator X-arm and the elevator control arm. These are both parallelagrams and need to remain such to keep binding out of the system. Adjusting it between the X-arm and the servo will cause minimal binding if any at all.

Malorie

[cbergen]

Mal is 100% correct, better to adjust the long elevator servo rods to straighten it up than the elevator yoke ball links.

[ShawnK]

Okee dokee, well there you have it.